In the case of such a longitudinal guide on each lower rail a slidable upper rail is disposed such that both rails form profile a substantially rectangular cross-section in their functional position, wherein bearing areas of the upper rail are formed on the lower rail as an embracing portion, which are disposed at the two corner areas of the rail profiles essentially diagonally opposite to each other and which have associated guiding means, wherein end portions of the lower rail and of the upper rail are respectively formed as essentially U-shaped profiles in the bearing areas, which are engaged with each other.
WO 2006/106044 A1 of the Applicant discloses such a longitudinal guide, wherein a first upper bearing area, which uses a plurality of balls as guiding means, and a second lower bearing area, which is diagonally opposite to the first bearing area and uses as guiding means a combination of rollers for supporting on a base leg of the lower rail and balls, are biased against each other in diagonal direction in order to accomplish a high rigidity of the rail profile. The balls in the first bearing area are mounted between two circular arc-shaped profiles, wherein one of the circular arc-shaped profiles forms a corner area at the upper end of a connecting leg of the lower rail, which is upwardly inclined at an acute angle and projects outwards relative to the rail.
Despite advantageous characteristics of this rail profile, there is still room for further improvement, particularly as in terms of the installation space available for this purpose, the total width and the width at the lower end of the rail profile as well as in terms of rigidity and the material or total weight required to implement it. Important in this context are particularly mechanical characteristics, especially the rigidity and torsional rigidity of the rail profile in the event of a crash, be it a frontal or rear crash or a side crash.
DE 197 17 667 A1 discloses a further longitudinal guide for motor vehicle seats, wherein the end portions of the upper rail, which end in the bearing areas that are diagonally opposite to each other, are formed with multiple curved section so that in each embracing portion respective two channels for balls are provided, if viewed in a cross sectional view, which act as guiding means. Precise formation of such end portions can be accomplished only in a relatively complicated manner, so that the tolerances are relatively high. The play of the longitudinal guide is further enlarged due to the higher wear, which results from the point contact of the ball-bearing guides.
JP 2004 203264 A discloses a further longitudinal guide for a motor vehicle seat, wherein a second bearing area in the sense of the present application is provided but not at the same time a ball guide and a roller guide, but instead two ball guides. There exists no supporting leg, which is associated to the upper ball bearing and which includes an acute angle with another supporting leg. Rather, the ball is received in an arcuately shaped longitudinal bead.
EP 1 336 765 A discloses a longitudinal guide with double pairs of ball guides in each bearing area.
Further prior art is disclosed in the documents EP 1 621 390 A, DE 10 2004 061140 A, FR 2 872 102 A and US 2005/285008 A.